The miniaturization of electronic devices has been accompanied by advances in miniaturization and higher performance of the electronic components used therein, while at the same time, the assembly of electronic devices involves automatic mounting of electronic components on printed circuit boards. Such chip-type electronic components to be surface-mounted are housed in carrier tapes having receiving pockets thermoformed to the shapes of the electronic components formed consecutively thereon. After housing the electronic components in these receiving pockets, a cover tape is laid as a lid member over the top surface of the carrier tape, and the edges of the cover tape are continuously heat-sealed in the longitudinal direction using a heated sealing iron to form electronic component packages.
Cover tapes are cut to the widths of the carrier tapes to be heat sealed and wound continuously into rolls that are set in cover tape drawing portions of taping machines. When drawing out the cover tape, if the cover tape becomes stuck together front to back, resulting in the state generally known as blocking, then the cover tape cannot be stably drawn, and this can result in problems such as the components not being able to be stably loaded into the receiving pockets in the carrier tape, forcing the component loading line to stop. In other words, if cover tape is exposed to high-temperature or high-temperature high-humidity environments during transport or storage in roll form, they may undergo blocking in which the substrate layers on the front side or antistatic layers on the surface adhere to adhesive layers on the back side, and once blocking occurs, it usually cannot be undone even when the rolls are stored in a location where the temperature and humidity are controlled to be in an appropriate range. Additionally, depending on the type of resin constituting the adhesive layer, in addition to stopping the component loading line as mentioned above, there may be defects such as reduced antistatic performance due to the antistatic layer laminated on the substrate layer of the cover tape being transferred to the adhesive layer.
As countermeasures against blocking of cover tape, methods of adding an anti-blocking agent such as tin oxide, silica or aluminum silicate to the adhesive layer of cover tape (see Patent Documents 1-3), a method of adding an inorganic filler such as silica to an adhesive layer consisting of a polymethacrylic acid, polyester, polyurethane or vinyl chloride-vinyl acetate copolymer resin (see Patent Document 4) as well as a method of forming an antistatic anti-blocking layer consisting of a composition having a quaternary ammonium salt-type cationic surfactant dispersed in a urethane resin, an acrylic resin or a polyester resin (see Patent Document 5) have been proposed. However, these inventions provide insufficient blocking resistance when exposed to high-temperature or high-temperature high-humidity environments during transport or storage in the form of rolls.
In recent years, surface-mounted electronic components such as IC's, including transistors, diodes, capacitors and piezoelectric resistors, are inspected by inspection equipment for the presence or absence of electronic components, orientation of the components and lost or bent leads during the loading process. However, since most plastics have high electrical insulation properties, static electricity can easily accumulate and attract dust to the surface, which can prevent electronic components contained therein from being viewed clearly and force stoppages of the production line.
As a countermeasure against the above problem, an antistatic agent is often applied to the outermost surface of the cover tape.
As examples of antistatic agents that are commonly used, there are low molecular weight and polymeric antistatic agents such as surfactants that provide effects by adsorbing moisture from the air, but low molecular weight types may not be capable of obtaining sufficient antistatic performance to control adhesion of dust and particles which can be transferred to the surface opposite the coated surface when the tape is wound, thus having a detrimental influence on the performance. (Patent Document 6). Additionally, polymeric antistatic agents are susceptible to the influence of ambient humidity and moisture, and have reduced antistatic performance in low-humidity environments (in a 23° C.×20% RH atmosphere) (Patent Documents 7 and 8), making it difficult to maintain a sufficient antistatic performance.
Patent Document 1: JP H8-119373 A
Patent Document 2: JP 2000-280411 A
Patent Document 3: JP 2011-63662 A
Patent Document 4: JP 2000-327024 A
Patent Document 5: JP 2004-51105 A
Patent Document 6: JP 2009-40835 A
Patent Document 7: JP 2010-132927 A
Patent Document 8: JP 2008-296447 A